FBX Binary format - Nested Nodes
Everything is explained here, in Node Record Format section. Below I’m just rephrasing that document:


The first four bytes are an uint32, the total size (in bytes) of the node.
The next four bytes are an uint32, the total number of properties.
The next four bytes are an uint32, the total size (in bytes) of properties (aka propertieslen).
The next byte is a uint8, the total size (in bytes) of the node name (aka namelen).
Then you have the node name itself.
Then you have the properties.
Then you have the nested list of sub-nodes.
Then you have the final 13 NULL bytes.


So, you know nested subnodes (if any) start at 4 + 4 + 4 + 1 + &lt;namelen&gt; + &lt;propertieslen&gt; bytes from beginning of current node. This is your “opening bracket”.

If you can “read” python, you can also have a look to our FBX addon code, in particular parse_fbx.py and fbx2json.py, that code is fairly simple and short, and illustrate well how to parse binary FBX.